As is well known in the industry, linear voice coil actuator s can be used for a variety of tasks. Included in these tasks are the measuring of components, the positioning and retrieval of parts, and other manufacturing activities in general. For all of these tasks it is an industry standard that the voice coil actuator must be generally capable of generating a one hundred kilogram force on a continuous basis for extended periods of time. Preferably, this can be done with less than two amperes of current. Further, it is very desirable for a voice coil actuator to be robust, accurate and reliable. Another, very important characteristic of a voice coil actuator is that it be compact. This is particularly so where manufacturing operations require the simultaneous use of many actuators. Together with these considerations, it is of utmost importance that the actuator not be prone to failures.
Heretofore, in the effort to balance the need for relatively large forces (e.g. 100 kg), with the desire for a small compact actuator, the typical solution has been to run the actuator at high current levels. The number one reason for the field failure of a voice coil actuator, however, is coil "burn out." As is well known, "burn out" results when efforts are taken to either increase the forces that can be generated by the actuator, or to extend the duration of its operational cycle. To accomplish these objectives, it has been the practice to apply excessive current to the coil of the actuator. When excessive currents are run through a coil, however, excessive heat is generated. In time, this heat causes the wire insulation to melt and short out the coil, or it causes the coil to deform which can also cause a short. Another problem arises when the coil deforms and bulges due to the excessive heat that is generated by the excessive current. In a voice coil actuator, such a deformation of the coil can cause the coil to contact other metallic parts of the actuator. When this happens, a short can result. The consequence in either case is a failure of the voice coil actuator.
Several solutions have been proposed for the problems noted above. These include: 1) the incorporation of thermistors which will alert the operator to damaging heat levels in the actuator; 2) the use of fans for cooling the actuator during its operation; and 3) the establishment of limited duty cycles for actuator operation which will require the actuator be given a "rest" for predetermined shut down periods. All of these solutions, however, have their shortcomings and are generally of questionable efficiency.
In light of the above it is an object of the present invention to provide a method for manufacturing a linear voice coil actuator which can generate as much as one hundred kilograms (100 kg) of force with no more than approximately 2 amperes of current running through its coil. Another object of the present invention is to provide a method for manufacturing a linear voice coil actuator which can be continuously operated for extended periods of time without "burning out" the coil. Yet another object of the present invention is to provide a linear voice coil actuator which is relatively easy to manufacture, is simple to operate and comparatively cost effective.